1. Field of the Invention
The present invention relates to a display device, and more particularly to a multiprimary display device which performs display by using four or more primary colors. The present invention also relates to a color filter substrate for use in such a display device.
2. Description of the Related Art
Currently, various display devices are used in a variety of applications. In commonly-used display devices, each pixel is composed of three subpixels for displaying three primaries of light (i.e., red, green and blue), whereby multicolor display is achieved.
A problem of conventional display devices is that they can only display colors in a limited range (referred to as a “color reproduction range” or a “color gamut”). FIG. 47 shows a color gamut of a conventional display device which performs display by using three primaries. FIG. 47 is an xy chromaticity diagram in an XYZ color system, where a color gamut is shown by a triangle whose apices are at three points corresponding to the three primaries of red, green and blue. Also shown in FIG. 47 are plotted colors (represented by “X” symbols) of various objects in nature, as taught by Pointer (see M. R. Pointer, “The gamut of real surface colors,” Color Research and Application, Vol. 5, No. 3, pp. 145-155 (1980)). As can be seen from FIG. 47, there are some object colors which do not fall within the color gamut. Thus, display devices which perform display by using three primaries are unable to display certain object colors.
Therefore, in order to expand the color gamut of a display device, there has been proposed a technique which increases the number of primary colors to be used for displaying to four or more.
For example, as shown in FIG. 48, Japanese National Publication No. 2004-529396 (hereinafter, “Patent Document 1”) discloses a liquid crystal display device 800 each of whose pixels P is composed of six subpixels R, G, B, Ye, C and M for displaying red, green, blue, yellow, cyan, and magenta, respectively. The color gamut of the liquid crystal display device 800 is shown in FIG. 49. As seen from FIG. 49, a color gamut which is represented as a hexagonal shape whose apices are at six points corresponding to the six primary colors substantially encompasses all object colors. Thus, the color gamut can be expanded by increasing the number of primary colors to be used for displaying. In the present specification, any display device which performs display by using four or more primary colors will be generally referred to as a “multiprimary display device”.
However, the inventors have performed a detailed study concerning the display quality of multiprimary display devices, and thus found that sufficient display quality cannot be achieved by merely increasing the number of primary colors. For example, in accordance with the display device disclosed in Patent Document 1, the actually-displayed red colors will appear blackish (i.e., dark red), which means that there actually exist some object colors that cannot be displayed.